EP0028484B1

EP0028484B1 - Process for the preparation of active-type vitamin d3 compounds and of the cholesta-5,7-diene precursors, and products so obtained

Info

Publication number: EP0028484B1
Application number: EP80303732A
Authority: EP
Inventors: Osamu Nishikawa; Kenji Ishimaru; Toru Takeshita; Hideki Tsuruta
Original assignee: Teijin Ltd
Current assignee: Teijin Ltd
Priority date: 1979-10-23
Filing date: 1980-10-22
Publication date: 1985-08-14
Also published as: US4388243A; EP0028484A1; DE3070985D1; DK160817B; CA1160217A; DK447380A; DK160817C

Description

The present invention relates to a novel process for the preparation of active-type vitamin D₃ compounds and their intermediates. More particularly, the present invention relates to a novel process for the preparation of active-type vitamin D₃ compounds including la-hydroxycholecalciferol, 1a,24-dihydroxycholecalciferol, 1a.,25-dihydroxycholecalciferol and the like,which are used for controlling the calcium metabolism in warm-blooded animals, and their intermediates in high yield, thus being of highly industrial value.
Up to now, active-type vitamin D₃ compounds, for example, la-hydroxycholecalciferol or the like, have been prepared, for example, as described in Japanese patent laid open No. 48-62570 or Tetrahedron Letters 40 4147―4150 (1972), by starting from a hydroxycholest-5-ene having hydroxyl groups protected with acetyl groups, for example, 1α-3β-(diacetoxycholest-5-ene, 1α,3β,24-triacetoxycholest-5-ene or the like, the allylic bromination and subsequent dehydrobromination to form the corresponding hydroxycholesta-5,7- diene, the irradiation of the product with ultraviolet rays, the thermal isomerization, and the elimination of the protecting groups.
Further, Chem, Pharm, Bull, 23 685―697 (1975) and others describe another method of the preparation of active-type vitamin D₃ compounds that starts from a hydroxycholest-5-ene protected with benzoyl groups and comprises the steps of allylic bromination and dehydrobromination to form the corresponding hydroxycholesta-5,7-diene, the irradiation of the product with ultraviolet rays and the thermal isomerization.
However, in these processes, the allylic bromination of a hydroxycholest-5-ene followed by dehydrobromination gives the corresponding hydroxycholesta-5,7-diene in an isolation yield as low as 15 to 30% and the yield reproducibility is low. Further, since the relatively high proportion of a hydroxycholesta-4,6- diene formed as a by-product in the reaction mixture causes difficulty to isolate the requisite hydroxy- cholesta-5,7-diene, they can not be regarded as satisfactory processes for the preparation of active-type vitamin D₃ compounds.
In the meantime, conventional steps of ultraviolet irradiation and thermal isomerization reaction as the final stage for the preparation of active-type vitamin D₃ compounds give unsatisfactorily very low yield.
For example, according to an example in the specification of Japanese patent laid open No. 48-62750, the irradiation of 600 micrograms of 1α,3β-diacetoxycholesta-5,7-diene with ultraviolet rays forms only 120 micrograms of 1α,3β-diacetoxyprevitamin D₃ and the specification of Japanese patent laid open No. 51-110554 describes that 135 milligrams of 1α,3β-diacetoxycholesta-5,7-diene is led to only 13 milligrams of la-hydroxycholecarciferol and 8 milligrams of la-hydroxyprevitamin D₃.
Japanese patent laid open No. 51-108050 and 53-87344 describe another process for the preparation of active-type vitamin D₃ compounds in which the irradiation of a hydroxycholesta-5,7-diene with ultraviolet rays is stopped when the conversion of the hydroxycholesta-5,7-diene reaches about 50% to prevent the corresponding previtamin D₃ formed by the irradiation from further converting to other compounds, for example, corresponding tachysterol, lumisterol and others, the unreacted hydroxy- cholesta-5,7-diene is separated from the previtamin D₃ and recycled to the irradiation step, and the previtamin D₃ is thermally isomerized and eliminated the protecting groups.
However, in the above process, the separation of the previtamin D₃ from the unreacted hydroxy- cholesta-5,7-diene after ultraviolet irradiation is effected by high-speed liquid chromatography, which has a possibility to decompose the previtamin D₃ during the operation because of its unstability. Further, high-speed liquid chromatography can not treat a large amount of compounds at a time and so is not always satisfactory as an industrial procedure for the preparation of active-type vitamin D₃ compounds.
An object of the present invention is to provide an excellent process for the preparation of hydroxy- cholesta-5,7-diene series, the intermediates of active-type vitamin D₃ compounds.
Another object of the present invention is to propose industrially excellent steps for the ultraviolet irradiation and thermal isomerization, the final stage for the preparation of active-type vitamin D₃ compounds.
Further, another object of the present invention is to propose an industrially excellent sequence of steps for the preparation of active-type vitamin D₃ compounds.
Other objects of the present invention will become apparent from the description which follows.
The objects and advantages of the present invention mentioned above can be accomplished by adopting a new synthetic path way described below.
Namely, the new synthetic path way is for the preparation of hydroxycholesta-5,7-dienes of the following formula [II]
wherein R, and R₂ represent a lower alkoxycarbonyl group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group or a hydroxyl group,
which comprises reacting hydroxycholest-5-enes of the following formula [I]
wherein R_i, R₂, R₃ and R₄ are the same as defined above,
with an allylic brominating agent in an inert organic solvent, and then contacting the resulting reaction mixture with a dehydrobrominating agent..
In the process of the present invention, a hydroxycholest-5-ene having hydroxyl groups protected with lower alkoxycarbonyl groups is used as a starting material and the employment of such a compound enables the efficient formation of hydroxycholesta-5,7-dienes in high yield by restraining the transformation to hydroxy-4,6-dienes, a by-product. Further, the resulting hydroxycholesta-5,7-dienes protected with lower alkoxycarbonyl groups permits highly efficient ultraviolet irradiation and thermal isomerization, which are the final stages in the preparation of active-type vitamin D₃ compounds. The hydroxycholest-5-enes and hydroxycholesta-5,7-dienes mentioned above have not been described in literatures, being novel compounds that have been synthesized by the present inventors for the first time.
In the aforesaid formula [I], R, and R₂ are lower alkoxycarbonyl groups, R₃ is a hydrogen atom or lower alkoxycarbonyloxy group and R₄ is a hydrogen atom, lower alkoxycarbonyloxy or hydroxyl group. By "lower alkoxycarbonyl" we mean alkoxycarbonyl groups having up to 4 carbon atoms in the alkoxy group. Suitable lower alkoxycarbonyl groups in the present invention include methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, and so forth and methoxycarbonyl or ethoxycarbonyl groups is most preferred. As R₄ is a tertiary substituent and undergoes steric hindrance, the reactivity is low and it exerts little effect on the reaction course of the preparation of hydroxycholesta-5,7-dienes. Consequently in the present invention R₄ includes free hydroxyl group too.
Specific examples of cholest-5-enes of formula (I) are as follows:

(1) 1α,3β-diethoxycarbonyloxycholest-5-ene,
(2) 1α,3β-dimethoxycarbonyloxycholest-5-ene,
(3) 1α,3β24-triethoxycarbonyloxycholest-5-ene,
(4) 1α,3β24-trimethoxycarbonyloxycholest-5-ene,
(5) 1α,3β25-triethoxycarbonyloxycholest-5-ene,
(6) 1 α,3β25-trimethoxycarbonyloxycholest-5-ene,
(7) 1α,3β,24,25-tetraethoxycarbonyloxycholest-5-ene,
(8) 1α,3β,24,25-tetramethoxycarbonyloxycholest-5-ene,
(9) 1a,3a-diethoxycarbonyloxy-25-hydroxycholest-5-ene, and
(10) 1α,3β-dimethoxycarbonyloxy-25-hydroxycholest-5-ene.

Said hydroxycholest-5-enes of formula (I) are readily prepared by, for example, reaction between hydroxycholest-5-enes having free hydroxyl groups and ethyl chloroformate in the presence of a catalyst of tertiary amine, for example, 4-dimethylaminopyridine. The reaction proceeds at room temperature to 80°C. Since ethyl chloroformate boils at a low temperature, some caution is required during the reaction and the desirable reaction time is usually 20 to 30 hours.
The resulting hydroxycholest-5-enes having hydroxyl groups protected with lower alkoxycarbonyl group are subjected to reactions with an allylic brominating agent and subsequently with a dehydrobrominating agent to give requisite hydroxycholesta-5,7-dienes, intermediates of active-type vitamin D₃ compounds.
In the present invention any usual allylic brominating agent may be employed and suitable brominating agents include N-bromosuccimide, 1,3-dibromo-5,5-dimethylhydantoin, N-bromocapro- lactam and the like. The amount of these allylic brominating agent used is usually 1 to 2 times the molar quantity of the starting hydroxycholest-5-enes of formula (I).
The allylic bromination in the present invention is effected by making an allylic brominating agent act on a hydroxycholest-5-ene of formula (I) in an inert organic solvent wherein the suitable temperature is room temperature to 140°C.
The inert organic solvent is required to be unreactive with the allylic brominating agent. Suitable inert organic solvents include hydrocarbons and halogenated hydrocarbons such as hexane, heptane, cyclohexane, ligroin, benzene, toluene, xylene, bromobenzene, chlorobenzene, nitrobenzene, carbon tetrachloride 1,2-dichloroethane, or 1,2-dibromoethane.
Further, ethereal solvents, for example, ethyl ether, tetrahydrofuran, dioxane, methylcellosolve or phenylcellosolve, are also employed.
These inert organic solvents may be used alone or in form of mixture.
The reaction proceeds at aforementioned temperatures, however, active rays of wave length in the region from infrared to ultraviolet may be irradiated in the brominating reaction. In such a case, the reaction proceeds even at a lower temperature than room one. Further, a small amount of radical initiator such as azobisisobutyronitrile, benzoyl peroxide or cyclohexenyl hydroperoxide may be added.
The brominated hydroxycholest-5-enes resulting from the above reaction is made to contact with a dehydrobrominating agent and transformed to corresponding hydroxycholesta-5,7-dienes of formula (II).
In this reaction, the reaction solvent is not always necessary, because some dehydrobrominating agents can serve as a reaction solvent as they are. In cases where reaction solvents are employed, as a solvent suitable for the dehydrobromination is not always the same as that suitable for the preceding bromination, the dehydrobromination is usually effected in a newly added solvent after removal of the solvent employed in the preceding reaction.
Suitable reaction solvents include xylene, bromobenzene, chlorobenzene, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, and so forth.
Suitable dehydrobrominating agents includes trimethyl phosphite, S-collidine, diethylaniline and the like and they may be combined. Theoretically, the equimolar amount of an agent is sufficient to cause the reaction, however, desirable reaction rate and yield are attained when about two or more moles are used for each mole of said brominated compound. As described above, some dehydrobrominating agents serve also as a reaction solvent and there is no specified upper limit in the amount employed.
The reaction usually proceeds at a temperature of from 100° to 180°C suitably. The reaction time depends upon the dehydrobrominating agent and reaction solvent, however, in a preferable example where the reaction is effected in xylene-S-collidine system under reflux, the reaction reaches completion in a short time of about 20 minutes.
After completion of the reaction, the reaction product, corresponding hydroxycholesta-5,7-dienes, is separated and purified by removing the solvent from the reaction mixture and recrystallizing the iresidue.
The preparation of hydroxycholesta-5,7-dienes starting from hydroxycholest-5-enes having hydroxyl groups protected with lower alkoxycarbonyl groups in accordance with the present invention results in higher yield as compared with to conventional processes and reduces the proportion of hydroxycholesta-4,6-dienes formed as a by-product. Additionally, the protecting group of lower alkoxycarbonyl increases the crystallizability of the requisite compound. The merit of this invention provides a great advantage that the isolation and purification of hydroxycholesta-5,7-dienes resulting from the aforementioned allylic bromination and dehydrobromination can be readily effected by a simple method of recrystallization.
The recrystallization is conducted preferably by a conventional method using a mixed solvent consisting of lower aliphatic alcohol such as methanol, ethanol, n-propanol, isopropanol, n-butanol, methoxyethanol, n-hexanol or the like and lower aliphatic ether such a dimethyl ether, diethyl ether, diisopropyl ether, tetrahydrofuran, dioxane, 1,2-dimethoxyethane or the like.
In this manner mentioned above, are prepared hydroxycholesta-5,7-dienes including 1α,3β-diethoxy- carbonyloxycholesta-5,7-diene, 1a,3a-dimethoxycarbonyloxycholesta-5,7-diene, 1a,3(3,24-triethoxy- carbonyioxychoiesta-5,7-diene, 1α,3β,24-trimethoxycarbonyloxycholesta-5,7-diene, 1 a,₃ ^p,25-triethoxy- carbonyloxycholesta-5,7-diene, 1a,3(3,25-trimethoxycarbonyloxycholesta-5,7-diene, 1a,3p-diethoxy- carbonyloxy-25-hydroxycholesta-5,7-diene and so forth in high efficiency. The resulting hydroxycholesta-5,7-dienes are subjected to the ultraviolet irradiation and thermal isomerization reaction, which are the final stage for the preparation of active-type vitamin D₃ compounds.
The present invention involves two kinds of ways as the final stage as follows:

(A). A process for preparing active-type vitamin D₃ compounds of the following formula [IV]
wherein R₃' and R₄' independently represents a hydrogen atom or a hydroxyl group, which comprises:
- (i) exposing hydroxycholesta-5,7-dienes of the following formula [II]
  wherein R₁ and R₂ represent a lower alkoxycarbonyl group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group or a hydroxyl group, to ultraviolet irradiation in an inert organic solvent to obtain the mixture of previtamin D₃ compounds, of the following formula [III]
  wherein R₁, R₂, R₃ and R₄ are the same as defined above,
and the unchanged hydroxycholesta-5,7-dienes of the formula [II];
- (ii) separating the mixture into the previtamin D₃ compounds and the unchanged hydroxycholesta-5,7- dienes;
- (iii) recycling the unchanged hydroxycholesta-5,7-dienes through the ultraviolet irradiation; and
- (iv) thermally isomerizing the previtamin D₃ compounds and splitting off the protective groups.
(B) A process for preparing active-type vitamin D₃ compounds of the following formula [IV]
wherein R₃' and R₄' represent a hydrogen atom or a hydroxyl group, which comprises:
- (i) exposing hydroxycholesta-5,7-dienes of the following formula [II]
  wherein R, and R₂ represent a lower alkoxycarbonyl group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group or a hydroxyl group,
to ultraviolet irradiation in an inert organic solvent, then thermally isomerizing to obtain the mixture of protected active-type vitamin D₃ compounds of the following formula [V]
wherein R₁, R₂, R₃ and R₄ are the same as defined above,
and the unchanged hydroxycholesta-5,7-dienes of the formula [III];
- (ii) separating the mixture into the protected active-type vitamin D₃ compounds and the unchanged hydroxycholesta-5,7-dienes;
- (iii) recycling the unchanged hydroxycholesta-5,7-dienes through the ultraviolet irradiation; and
- (iv) splitting off the protective groups of the protected active-type vitamin D₃ compounds

According to method (A) or (B), the ultraviolet irradiation and thermal isomerization are effected in high efficiency and yield by simple operations, thus being adaptable to large scale commercial production.
Consequently, according to the present invention, are provided industrially excellent procedures for the ultraviolet irradiation and thermal isomerization, which are the final stage for the preparation of active-type vitamin D₃ compounds, and an industrially excellent sequence of steps for the preparation of active-type vitamin D₃ compounds starting from the hydroxycholesta-5-enes.
In the ultraviolet irradiation in accordance with methods (A) and (B), the ultraviolet rays employed range in wave length from about 200 to 360 millimicron, preferably from 260 to 310 millimicron.
As a reaction solvent, an inert organic solvent is preferred and suitable solvents include hydrocarbons and halogenated hydrocarbons such as hexane, heptane, cyclohexane, ligroin, benzene, toluene, xylene, bromobenzene, chlorobenzene, nitrobenzene, carbon tetrachloride 1,2-dichloroethane, 1,2-dibromoethane or the like, ethereal solvents such as diethyl ether, tetrahydrofuran, dioxane, methylcellosolve, phenylcellosolve or the like and alcoholic solvents such as methanol, ethanol, propanol, hexanol, cyclohexanol or the like. Especially benzene, toluene, diethyl ether, methanol and ethanol are preferred and they are used alone or in form of mixture.
The ultraviolet irradiation is effected at temperatures of from -20° to 120°C and the range from -10° to 20°C is especially preferred. Further, the irradiation is preferably effected under an oxygen-free inert atmosphere of argon or nitrogen gas.
In the methods A and B of the present invention, the ultraviolet irradiation is desirably stopped at a level of low conversion of hydroxycholesta-5,7-dienes and especially the ultraviolet irradiation is preferably stopped at a level of 0.1 to 50% conversion, much preferably 10 to 40%, and most preferably 10 to 30%. The discontinuation of ultraviolet irradiation at a low conversion supresses the further undesirable converting of the previtamin D₃ compounds of formula (III) formed by the irradiation to useless other compounds, for example, corresponding lumisterols and tachysterols, resulting in increase in the proportion of the previtamin D₃ compounds formed.
As a result, the ultraviolet irradiation gives a mixture of previtamin D₃ compounds and unreacted hydroxycholesta-5,7-dienes, from which, in method A, the products, previtamin D₃ compounds and the unreacted hydroxycholesta-5,7-dienes are isolated.
According to method A of the present invention, a hydroxycholesta-5,7-dienes protected with lower alkoxycarbonyl groups is employed as a starting material and converted by ultraviolet irradiation to a mixture of previtamin D₃ and unreacted hydroxycholesta-5,7-diene, both of which have hydroxyl groups protected with lower alkoxycarbonyl groups. The resulting mixture of previtamin D₃ compounds and unreacted hydroxycholesta-5,7-dienes is readily separated by simple recrystallisation from or rinsing with an organic solvent, utilizing the difference in solubility between them, without aid of high-speed liquid chromatography. Thus, the process for the preparation of active-type vitamin D₃ compounds according to the present invention is capable of readily separating both compounds by simple procedures and provides a very large possibility of establishing an industrially high efficient method.
In the separation, after ultraviolet irradiation, a part of the reaction solvent is distilled off and the solid material or crystals formed is filtered by a usual method, whereby the reaction mixture is divided into crystals or the solid material of cholesta-5,7-dienes and filtrate containing previtamin D₃ compounds. Or after ultraviolet irradiation, the reaction solvent is distilled off and an alcoholic solvent such as methanol, ethanol, isopropanol, hexanol, cyclohexanol, or the like or a mixture thereof with an ethereal solvent such as diethyl ether, tetrahydrofuran, or the like is added to the residue to form solid materials or crystals, which are subjected to the same operations as mentioned above to separate the unreacted hydroxy- cholesta-5,7-dienes from the previtamin D₃ compounds.
The previtamin D₃ compounds formed by ultraviolet irradiation may be partially isomerized to the active-type vitamin D₃ compounds by heat energy, however, the active-type vitamin D₃ compounds formed is also separated together with the previtamin D₃ compounds in the above separation step.
The unreacted hydroxycholesta-5,7-dienes separated is recycled for reuse as a starting material and the previtamin D₃ compound is subjected to consequent thermal isomerization and splitting off the protective groups.
The thermal isomerization is preferably effected in an inert organic solvent and suitable solvents include the same ones as those which are used in the ultraviolet irradiation.
The thermal isomerization is an equilibrium reaction between a previtamin D₃ compound and the corresponding active-type vitamin D₃ compound. The equilibrium value varies with the reaction temperature and generally as the isomerization temperature rises higher, the isomerization reaction from previtamin D₃ to vitamin D₃ increases the rate, whereas the equilibrium value of vitamin D₃ shifts to the reduction side. In view of such situation, the isomerization reaction is effected at 20° to 120°C, preferably at 40° to 100°C.
The thermal isomerization reaction gives an active-type vitamin D₃ compounds protected with lower alkoxycarbonyl groups, which is subsequently isolated and purified or the thermal isomerization reaction, without isolation and purification, is followed by the splitting off the protective groups.
On the other hand, in the pesent invention, immediately after the ultraviolet irradiation, the resulting previtamin D₃ compounds may be subjected to the reaction of splitting off the protective groups followed by the thermal isomerization.
In method (B) of the present invention, the reaction mixture after ultraviolet irradiation, containing previtamin D₃ compound and unreacted hydroxycholesta-5,7-dienes, is directly subjected to thermal isomerization without separation from each other. The thermal isomerization is carried out under the same conditions as those in method A and suitable organic solvents include those which are preferably used in the ultraviolet irradiation in method A. The reaction temperature is 20° to 120°C, preferably 40° to 100°C.
In method (B), a mixture of active-type vitamin D₃ compound having protected hydroxyl groups of formula (V) and unreacted hydroxycholesta-5,7-dienes is obtained as the reaction product. Both of them, resulting active-type vitamin D₃ compound and unreacted hydroxycholesta-5,7-diene, which have lower alkoxycarbonyl groups as protective groups, are readily separated, as in method (A), by simple recrystallization from or rinsing with an organic solvent, utilizing the difference in solubility between them, without aid of high-speed liquid chromatography, into the active-type vitamin D₃ compounds having protected hydroxyl groups and unreacted hydroxycholesta-5,7-dienes.
In the separation, after thermal isomerization, a part of the reaction solvent is distilled off and the solid materials or crystals formed are filtered by a usual method, whereby the hydroxycholesta-5,7-dienes is collected as crystals or solid materials and the active-type vitamin D₃ compounds having protected hydroxyl groups is obtained in form of filtrate solution.
Or after thermal isomerization, the reaction solvent is distilled off and as in method A, an alcoholic solvent such as methanol, ethanol, isopropanol, hexanol, cyclohexanol, or the like or a mixture thereof with an ethereal solvent such as diethyl ether, tetrahydrofuran, or the like is added to the residue. The solid materials or crystals formed are subjected to the same operations as in method A, whereby the reaction mixture is similarly separated into active-type vitamin D₃ compounds having protected hydroxyl groups and the unreacted hydroxycholesta-5,7-dienes.
The protected active-type vitamin D₃ compounds formed by ultraviolet irradiation and thermal isomerization may be partially isomerized to the previtamin D₃ compounds at equilibrium reaction, however, the previtamin D₃ compounds formed is also separated together with the protected active-type vitamin D₃ compounds.
The unreacted hydroxycholesta-5,7-dienes separated is recycled for reuse as a starting material, meanwhile the active-type vitamin D₃ compounds having protected hydroxyl groups undergoes the deprotection reaction as in method (A). The reaction of splitting off the protective groups in itself is known and the protective groups are readily removed by contact with an alkali, for example, sodium hydroxide or potassium hydroxide.
The resulting active-type vitamin D₃ compounds is purified by a usual method, such as extraction, recrystallization, column chromatography, thin-layer chromatography, high-speed liquid chromatography and others.
Further, in the present invention, high-purity previtamin D₃ compounds or active-type vitamin D₃ compounds having protected hydroxyl groups is separated from a mixture of the unreacted hydroxy- cholesta-5,7-dienes and previtamin D₃ compounds or a mixture of the unreacted hydroxycholesta-5,7- dienes and active-type vitamin D₃ compounds having protected hydroxyl groups resulting from ultraviolet irradiation or combination of ultraviolet irradiation and thermal isomerization, and the high-purity product is provided for the subsequent reactions. Therefore, the final stage of isolation and purification of active-type vitamin D₃ compounds is readily effected by a relatively simple method, for example, extraction, recrystallization, chromatography and others.
Consequently, according to the present invention, active-type vitamin D₃ compounds, for example, 1α-hydroxycholecarciferol, 1a,24-dihydroxycholecarciferol, 1a,25-dihydroxycholecarciferol, which are known as a controller of calcium metabolism in warm-blooded animals, are prepared with industrial advantages.
As mentioned above, in accordance with the present invention, a large amount of an active-type vitamin D₃ compounds is efficiently prepared with high industrial advantages by very simple processes comprising of the allylic bromination of a hydroxycholest-5-enes, as a starting material, the dehydrobromination to corresponding hydroxycholesta-5,7-dienes in high yield, an intermediate of active-type vitamin D₃ compounds, the subsequent ultraviolet irradiation or a combination of the irradiation and thermal isomerization of the hydroxycholesta-5,7-dienes to a mixture of the unreacted hydroxycholesta-5,7-dienes and previtamin D₃ compounds or a mixture of the unreacted hydroxycholesta-5,7-dienes and active-type vitamin D₃ compounds having protected hydroxyl groups, the separation of the mixture by very simple operations such as crystallization or rinsing, the recycling of the unreacted hydroxycholesta-5,7- dienes recovered and the final thermal isomerization and protective group splitting off reaction of the remaining compounds, and the process for the preparation of active-type vitamin D₃ compounds in the present invention is of very high industrial value, capable of carrying out by simple operation and adaptable to large scale commercial production.
This invention is further illustrated by the following detailed examples.

Example 1

(1) Synthesis of 1a,3a-diethoxycarbonyloxycholest-5-ene

To a solution of la-hydroxycholesterol (10 g) and 4-dimethylaminopyridine (12 g) in methylenechloride (100 ml), was added ethyl chlorocarbonate (47.5 ml) with stirring at 0°C. After stirring for 28 hours at 60°C, the reaction mixture was poured into ice water and extracted with methylenechloride. The methylenechloride extracts were washed with 2N hydrochloric acid, saturated sodium bicarbonate solution and saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The drying agent was collected on a filter. The filtrate was concentrated under reduced pressure to give 13.34 g of residual product. The crude product was chromatographed on a column of silica gel (300 g) and the column was eluted with benzene-ethylacetate to give 12.6 g (yield; 93%) of 1α,3β-diethoxycarbonyloxycholest-5-ene.

(2) Synthesis of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene

A solution of 1a,313-diethoxycarbonyloxycholest-5-ene (5.46 g, 10 m moles), dry hexane (100 ml) and 1,3-dibromo-5,5-dimethylhydantoin (1.716 g, 6 m moles) was reacted at the oil bath temperature of 95°C under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting 5,5-dimethylhydantoin and the excessive 1,3-dibromo-5,5-dimethythydantoin were removed by filtration. The filtrate was concentrated at reduced pressure to afford a residual product. Xylene was added to this substance to form a solution. The resulting solution was added dropwise to a solution held at 170°C of s-collidine (25 ml) in dry xylene (33 ml), and the reaction was carried out for additional 20 minutes. Afterthe reaction, the hydrobromide of s-collidine was removed by filtration and the filtrate was concentrated under reduced pressure to give residual product. The residue was dissolved in ethyl acetate (200 ml). The ethyl acetate solution was washed with 1N hydrochloric acid (3 x 100 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 6.68 g of residual product.

(3) Separation of 1,3-diethoxycarbonyloxycholesta-5,7-diene

The residual product (6.68 g) obtained in (2) above was dissolved in the mixture of methanol (170 ml) and ether (10 ml) with heating at 80°C. The solution was allowed to cool to room temperature and permitted to stay at room temperature over night in the dark to give a white crystalline product. The product was separated by filtration, washed with methanol of 20°C, and dried under the reduced pressure in the dark to afford 3.41 g (62.5%) of crystals as white needles having the following characteristics.

Melting point (from a mixture of ether and methanol):
- 140.5-142°C
IR spectrum,
(cm^-1):
- 2950, 2860, 1740, 1465, 1370
NMR spectrum, δ ppm (CDCl₃):
- 0.62 (3H, s, C-18-CH₃),
- 0.86 (6H, d, C-26,27-CH₃X2),
- 1.31 (6H, t, C-1,3-CH₃X2 of ethoxycarbonyl groups),
- 4.20 (4H, q, C-1,3-CH₂X2 of ethoxycarbonyl groups),
- 4.86 (2H, b, C-1,3-HX2),
- 5.37, 5.67 (2H, b, C-6, 7-HX2)
UV spectrum (ethanol, λ_max, nm):
- 293 (e = 6760), 281 (s = 11530), 271 (s = 10800), 262 (shoulder s = 7580)
UV spectrum (ether, λ_max, nm):
- 293 (s = 7710), 281 (s = 13010), 271 (s = 123600), 262 (shoulder s = 8910).

Comparative Example 1

(1) Synthesis of 1α,3β-diacetoxycholesta-5,7-diene

A solution of 1α,3β-diacetoxycholest-5-ene (972 mg, 2 m moles), dry hexane (15 ml) and 1,3-dibromo-5,5-dimethyl hydantoin (343 mg, 1.2 m moles) was reacted at the oil bath temperature of 95°C under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting 5,5-dimethyl hydantoin and the excessive 1,3-dibromo-5,5-dimethylhydantoin were removed by filtration. The filtrate was concentrated at reduced pressure to afford a residual product. Xylene (6 ml) was added to this substance to form a solution. The resulting solution was added dropwise to a solution held at 170°C of s-collidine (5 ml) in dry xylene (6 ml), and the reaction was carried out for additional 20 minutes. After the reaction, the hydrobromide of s-collidine was removed by filtration and filtrate was concentrated under reduced pressure to give residual product. The residue was dissolved in ethyl acetate (30 ml). The ethyl acetate solution was washed with 1N hydrochloric acid (2 x 10 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 908 mg of residual product.

(2) Separation of 1a,3a-diacetoxycholesta-5,7-diene

The residue (908 mg, 1a,313-diacetoxycholesta-5,7-diene: 1α,3β-diacetoxycholesta-4,6-diene = 2:1, from the UV spectrum) was dissolved in the mixture of ether-hexane (1:10) with heating, allowed to cool to room temperature for 30 minutes, and permitted to stand in the dark at a temperature of 5°C for 14 hours. After standing, the solvent was removed by decontation, and the oily product was obtained, and washed with a cooled methanol, but not to afford a crystal. In the obtained oily product, the ratio of 5,7-diene to 4,6- diene was 2:1.

Example 2

(1) Synthesis of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene

To a solution of 1α,3β-diethoxycarbonyloxycholest-5-ene (2.73 g, 5 m moles) in dry hexane (50 m), 1,3-dibromo-5,5-dimethylhydantoin (858 mg, 3 m moles) was added dropwise under stirring and heating at oil bath temperature of 95°C, and the mixture was continued to react under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting precipitate was removed by filtration, the filtrate was concentrated at reduced pressure at 40°C to afford a residual product. Xylene was added to this substance to form a solution. The resulting solution was added dropwise to a solution held at 170°C of s-collidine (12.5 ml) in dry xylene (16.5 ml), and the reaction was carried out for additional 20 minutes. After the reaction, the resulting precipitate was removed by filtration and the filtrate was concentrated under reduced pressure at 40°C to give a residual product. The product was dissolved in ethyl acetate (100 ml). The ethylacetate solution was washed with 1 N hydrochloric acid (3 x 50 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 3.04 g of residual product.

(2) Analysis of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene

The product (3.04 g) obtained in (1) above was dissolved in ether (10 I). The resulting solution was subjected to the measurement of UV spectrum with a spectrophotometer (cell length; 1 cm, wavelength; 340 nm-200 nm). The UV spectrum showed, as maximum absorbance (λ_max), 293, 281, 271, 260 (shoulder), 249.4 (shoulder), 241 and 232. From the calculation based on the value of λ_max (281, e = 10250), the reaction yield in the step (1) above was determined to be 78.8%. On the other hand, from the ratio of absorbance in λ_max; 281 and λ_max; 240, the ratio (A5, 7/Δ4,6) of 1α,3β-diethoxycarbonyloxycholesta-5,7- diene to 1a,3a-diethoxycarbonyloxycholesta-4,6-diene was 5.25.

Comparative Example 2

(1) Synthesis of 1α,3β-diacetoxycholesta-5,7-diene

To a solution of 1α,3β-diacetoxycholest-5-ene (2.43 g, 5 m moles) in dry hexane (50 ml), 1,3-dibromo-5,5-dimethylhydantoin (858 mg, 3 m moles) was added dropwise under stirring and heating at oil bath temperature of 95°C, and the resulting mixture was continued stirring for 15 minutes under the irradiation of infrared rays. The reaction mixture was cooled, the precipitate filtered, and washed with hexane, and filtrate and washings were combined to give after evaporation of all solvents a residual product. Xylene was added to this substance to form a solution.
The resulting solution was added dropwise to a solution held at 170°C of s-collidine (12.5 ml) in dry xylene (16.5 ml), and the reaction was carried out for additional 20 minutes. The reaction mixture was cooled, the precipitate filtered, and washed with hexane, and filtrate and washings were combined. The combined solution was evaporate to afford a residual product. The residue was dissolved in ethylacetate (100 ml), washed with 1N hydrochloric acid (3 x 50 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 2.42 g of the crude product.

(2) Analysis of 1a,3(3-diacetoxycholesta-5,7-diene

The product (2.42 g) obtained in (1) above was dissolved in ether (10 I). The resulting solution was subjected to the measurement of UV spectrum with a spectrophotometer (cell length; 1 cm, wavelength; 340 nm-200 nm). The UV spectrum showed, as maximum absorbance (λ_max), 293.5, 281, 271, 260 (shoulder), 249, 239 and 228. From the value of λ_max (281, e = 8350), the reaction yield in the step (1) above was determined to be 64.2%. On the other hand, from the ratio of absorbance in À_max; 281 and 239, the ratio (A5.7/A4.6) was 3.23.

Example 3

(1) Synthesis of 1α,3β-dimethoxycarbonyloxycholesta-5,7-diene

To a solution of 1α,3β-dimethoxycarbonyloxycholest-5-ene (518 mg, 1 m mole) in dry hexane (10 ml), 1,3-dibromo-5,5-dimethylhydantoin (172 mg, 0.6 m moles) was added dropwise under stirring and heating at oil bath temperature of 95°C, and the mixture was continued to react under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting precipitate was removed by filtration, the filtrate was concentrated at reduced pressure at 40°C to afford a residual product. Xylene was added to this substance to form a solution. The resulting solution was added dropwise to a solution held at 170°C of s-collidine (2.5 ml) in dry xylene (3 ml), and the reaction was carried out for additional 20 minutes. After the reaction, the resulting precipitate was removed by filtration and the filtrate was concentrated under reduced pressure at 40°C to give residual product. The product was dissolved in ethylacetate (20 ml). The ethylacetate solution was washed with 1N hydrochloric acid (3 x 10 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 479 mg of residual product.

(2) Analysis of 1a,3a-dimethoxycarbonyloxycholesta-5,7-diene

The product (479 mg) obtained in (1) above was dissolved in ether (10 I). The resulting solution was subjected to the measurement of UV spectrum with a spectrophotometer (cell length; 1 cm, wavelength; 340 nm-200 nm). The UV spectrum showed, as maximum absorbance (λ_max), 293, 281, 271, 260 (shoulder), 249.5 (shoulder), 241 and 232. From the ratio of absorbance in λ_max; 281 and 240, the ratio (Δ5,7/Δ4,6) 1α,3β-dimethoxycarbonyloxycholesta-5,7-diene to 1α,3β-dimethoxycarbonyloxycholesta-4,6-diene was 4.34.

Example 4

(1) Synthesis of 1α,3β-diethoxycarbonyloxy-25-hydroxycholesta-5,7-diene

To a solution of 1α,3β-diethoxycarbonyloxy-25-hydroxycholesta-5-ene (562 mg, 1 m mole) in dry hexane (10 m), 1,3-dibromo-5,5-dimethyihydantoin (172 mg, 0.6 m moles) was added dropwise under stirring and heating at oil bath temperature of 95°C, and the mixture was continued to react under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting precipitate was removed by filtration, the filtrate was concentrated at reduced pressure at 40°C to afford a residual product. Xylene was added to this substance to form a solution. The resulting solution was added dropwise to a solution held at 170°C of s-collidine (2.5 ml) in dry xylene (3 ml), and the reaction was carried out for additional 20 minutes. After the reaction, the resulting precipitate was removed by filtration and the filtrate was concentrated under reduced pressure at 40°C to give residual product. The product was dissolved in ethylacetate (20 ml). The ethylacetate solution was washed with 1N hydrochloric acid (3 x 10 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 482 mg of residual product.

(2) Analysis of 1,3-diethoxycarbonyloxy-25-hydroxycholesta-5,7-diene

The product (482 g) obtained in (1) above was dissolved in ether (10 I). The resulting solution was subjected to the measurement of UV spectrum with a spectrophotometer (cell length; 1 cm, wavelength; 340 nm-200 nm). The UV spectrum showed, as maximum absorbance (λ_max), 293, 281, 271, 260 (shoulder), 249.5 (shoulder), 241 and 232. From the ratio of absorbance in λ_max; 281 and 240, the ratio (A5,7/A4,6) of 1α,3β-diethoxycarbonyloxy-25-hydroxycholesta-5,7-diene to 1α,3β-diethoxycarbonyloxy-25-hydroxy- cholesta-4,6-diene was 4.36.

Comparative Example 3

(1) Synthesis of 1α,3β,25-triacetoxycholesta-5,7-diene

To a solution of 1α,3β,25-triacetoxycholest-5-ene (544 mg, 1 m mole) in dry hexane (10 m), 1,3-dibromo-5,5-dimethyihydantoin (172 mg, 0.6 m moles) was added dropwise under stirring and heating at oil bath temperature of 95°C, and the mixture was continued to react under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting precipitate was removed by filtration, the filtrate was concentrated at reduced pressure at 40°C to afford a residual product. Xylene was added to this substance to form a solution. The resulting solution was added dropwise to a solution held at 170°C of s-collidine (2.5 ml) in dry xylene (3 ml), and the reaction was carried out for additional 20 minutes. After the. reaction, the resulting precipitate was removed by filtration and the filtrate was concentrated under reduced pressure at 40°C to give residual product. The product was dissolved in ethylacetate (20 ml). The ethylacetate solution was washed with 1N hydrochloric acid (3 x 10 ml), saturated sodium bicarbonate and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 473 mg of residual product.

(2) Analysis of 1a,313,25-triacetoxycholesta-5,7-diene

The product (473 mg) obtained in (1) above was dissolved in ether (10 I). The resulting solution was subjected to the measurement of UV spectrum with a spectrophotometer (cell length; 1 cm, wavelength; 340 nm-200 nm). The UV spectrum showed, as maximum absorbance (λ_max), 293, 281,271,260 (shoulder), 249.5 (shoulder), 241 and 232. From the ratio of absorbance in λ_max; 281 and 240, the ratio (A5,7/A4,6) of 1α,3β,25-triacetoxycholesta-5,7-diene to 1a,3a,25-triacetoxycholesta-4,6-diene was 2.57.

Example 5

(1) Synthesis of 1α,3β,24(R)-triethoxycarbonyloxycholest-5-ene

A ethyl chlorocarbonate (24.75 ml) was added dropwise to a solution of1a,3p,24(R)-trihydroxychoiest-5-ene (3.63 g), 4-dimethylaminopyridine (6.25 g) and methylenechloride (40 ml) with stirring at 0°C. After stirring for 27 hours at 60°C, the reaction mixture was poured into ice water and extracted with methylenechloride. The extracts were washed with 2N hydrochloric acid, saturated sodium bicarbonate solution and saturated sodium chloride solution, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 4.98 g of residual product. The residue was recrystallized from methanol (10 ml) to afford 3.64 g of 1α,3β,24(R)-triethoxycarbonoxycholest-5-ene as crystals.

(2) Synthesis of 1a,313,24(R)-triethoxycarbonyloxycholesta-5,7-diene

A solution of 1α,3β,24(R)-triethoxycarbonyloxycholest-5-ene (3.49 g, 5.5 m moles), dry hexane (58 ml) and 1,3-dibromo-5,5-dimethylhydantoin (998 mg, 3.3 m moles) was boiled under the irradiation of infrared rays for 15 minutes. The reaction mixture was cooled, and the resulting 5,5-dimethylhydantoin and the excessive 1,3-dibromo-5,5-dimethylhydantoin were removed by filtration. The filtrate was concentrated at reduced pressure to afford a residual product. Xylene was added to this substance to form a solution. The resulting solution was added dropwise to a solution held 170°C of s-collidine (14.5 ml) in dry xylene (19 ml), and the reaction was carried out for additional 20 minutes. After the reaction, the hydrobromide of s-collidine was removed by filtration and the filtrate was concentrated under reduced pressure at 40°C to give residual product. Thr residue was dissolved in ethylacetate (200 ml). The organic phase was washed with 1N hydrochloric acid (3 x 10 ml), saturated sodium bicarbonate solution and water, and dried over anhydrous sodium sulfate. The drying agent was removed by filtration and the filtrate was concentrated under reduced pressure to give 3.68 g of residual product.

(3) Separation of 1α,3β,24(R)-triethoxycarbonyloxycholesta-5,7-diene

The residual product (3.68 g) obtained in (2) above was dissolved in the mixture of methanol (7 ml) and ether (1 ml) with heating. The solution was allowed to cool to 5°C in the dark. The resulting product were collected by filtration, and dissolved in methanol (13 ml) with heating at 70°C for 30 minutes. The solution was cooled to room temperature, and moreover allowed to stand in the dark at 5°C for 1.5 hours to afford crystals as white needles. The crystals were collected by filtration, washed with methanol of 20°C, and dried under the reduced pressure in the dark to give 1.69 g (48.5%) of crystals as colorless needles having the following characteristics.

Melting point (from methanol): 116-117°C
UV spectrum (ethanol, λ_max, nm):
- 262 (8110), 271 (11410), 281 (12130), 293 (7200)
NMR spectrum, 6 ppm (CDCI₃):
- 0.62 (3H, s, C-18-CH₃),
- 1.31 (9H, t, C-1,3 and 24-CH₃x3 of ethoxycarbonyl),
- 4.18 (6H, q, c-1,3 and 24-CH₂x3 of ethoxycarbonyl),
- 4.50 (1H, bm, C-24-H),
- 4.80 (2H, bm, C-1,3-Hx2),
- 5.35, 5.65 (2H, bm, C-6-H and C-7-H).

Example 6

(1) Synthesis of 1α-ethoxycarbonyloxyprecholecalciferol-3β-ethoxycarbonate

272 mg (0.5 m moles of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 5 minutes at 10°C in an atmosphere of argon using a 200 W high pressure mercury lamp, 654A-36, trademark for a product of Hanovia Company, (Conversion 28%).
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure to give a residual product. Methyl alcohol (20 ml) cooled at 0°C was added to the residue. The residue was supended to afford crystals, and the resulting crystals, 173 mg of 1α,3β-diethoxycarbonyloxycholesta-5,7- diene, were removed by filtration. The filtrate was concentrated at 25°C under reduced pressure to afford the oily residue containing 1α-ethoxycarbonyloxyprecholecalciferol-3β-ethoxycarbonate. This product was used as the starting material in the next step without purification.

(2) Synthesis of 1α-ethoxycarbonyloxycholecalciferol-3β-ethoxycarbonate

1α-ethoxycarbonyloxyprecholecalciferol-3β-ethoxycarbonate obtained in (1) above, was dissolved in 100 ml of benzene, and isomerization was carried out for 14 hours at 50°C in an atmosphere of argon. After the reaction, the benzene was evaporated off at 25°C under reduced pressure to afford the oily residue containing 1α-ethoxycarbonyloxycholecalciferol-3β-ethoxycarbonate. This crude product was used as the starting material in the next step (3) without purification.

(3) Synthesis of la-hydroxy cholecalciferol

1a-ethoxycarbonyloxy cholecalciferol-313-ethoxycarbonate described above was dissolved in a mixture of 5 ml of methyl alcohol and 5 ml of benzene, and 5 ml of 2N-methyl alcohol solution of potassium hydroxide was added dropwise. After the addition, the reaction was carried out at 60°C for 1 hour.
The reaction mixture was concentrated at 25°C under reduced pressure to afford a residual product. 50 ml of water was then added to the residue and the product was extracted with ethyl acetate (50 ml x 2). The ethyl acetate extracts were combined, washed with a dilute hydrochloric acid, a saturated aqueous solution of sodium carbonate and a saturated aqueous solution of sodium chloride, dried over anhydrous sodium sulfate, filtered, and evaporated off at reduced pressure to afford 76 mg of the oily residue containing 1o-hydroxycholecalciferol. This crude product was column-chromatographed using silica gel (eluted with a benzeneacetone mixed solvent) to afford 22 mg of 1α-hydroxycholecalciferol (yield; 30%, based on 99 mg of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene used up).
This product showed the same characteristics as an authentic 1a-hydroxycholecalciferol.

Melting point:
- 14G-141°C (from a mixture of ether and n-hexane)
IR spectrum,
(cm^-1):
- 3400, 2950, 2890, 1640, 1630, 1470, 1450, 1380, 1055, 895, 795
NMR spectrum, 5 ppm (CDCI₃):
- 0.55 (3H, s, C-18-CH₃),
- 0.87 (6H, d, J=6.4 Hz, C-26 and 27-CH₃X2),
- 0.93 (3H, d, J=4.8 Hz, C-21-CH₃),
- 4.22-4.45 (2H, m, 1β-and 3a-proton),
- 5.00, 5.33 (1H, 1H, s, s, C-19-2H, vinyl proton),
- 5.95, 6.44 (1H, 1H, d, J=11.5 Hz, C-6-H, C-7-H),
Mass spectrum:
- M⁺ 400, 382, 364, 349, 287, 269, 251.

Example 7

(1) Synthesis of 1α-ethoxycarbonyloxyprocholecalciferol-3β-ethoxycarbonate

(a) The first reaction:-

272 mg (0.5 m moles) of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 5 minutes at 10°C in an atmosphere of argon using a 200 W. high pressure mercury lamp, 654A-36, trademark for a product of Hanovia Company (conversion: 30%)
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure.
Using a 272 mg (0.5 m moles) of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene, the same reaction as mentioned above was conducted three times.
The obtained residues in these reaction were put together, and methyl alcohol (80 ml) cooled at 0°C was added to the residues.
The residue was suspended to afford crystals and the resulting crystals, 664 mg of 1a,3p-diethoxy- carbonyloxycholesta-5,7-diene, were removed by filtration.
The filtrate was concentrated at 25°C under reduced pressure to afford the oily residue containing 1a-ethoxycarbonyloxy-pre-cholecalciferol-3β-ethoxycarbonate. This residue was named as L-No.1.

(b) The second reaction:-

120 mg of 1a,313-diethoxycarbonyloxycholesta-5,7-diene recovered in the first reaction (a) was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 2.5 minutes at 10°C in an atmosphere of argon using a 200 W high pressure mercury lamp, 654 A-36 trademark for a product of Honovia Company (conversion; 30%).
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure.
544 mg (1 m mol) of 1a,313-diethoxycarbonyloxycholesta-5,7-diene, the remains of 1α,3β-diethoxy- carbonyloxy cholesta-5,7-diene recovered in the first step (a), was irradiated with two batches in the same way as described in the first reaction (a). The obtained residues in these reaction were put together, and methyl alcohol (50 ml) cooled at 0°C was added.
The residue was suspended to afford crystals, and the resulting crystals, 358. mg of 1a,3(3-diethoxy- carbonyloxycholesta-5,7-diene were removed by filtration.
The filtrate was concentrated at 25°C under reduced pressure to afford the oily residue containing 1 a-ethoxycarbonyloxy-pre-cholecalciferol-3β-ethoxycarbonate. This residue was named as L-No.2

(c) The third reaction:-

358 mg of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene recovered in the second reaction (b) was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 5 minutes at 10°C in an atmosphere of argon using a 200 W high pressure mercury lamp, 654A-36 trademark for a product of Hanovia Company (conversion, 30%).
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure to afford a residual product.
To the residue methyl alcohol (25 ml) cooled at 0°C was added.
The residue was suspended to afford crystals and the resulting crystals, 224 mg of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene, were removed by filtration.
After the filtration, the filtrate was concentrated at 25°C under reduced pressure to afford the oily residue containing 1α-ethoxycarbonyloxyprecholecalciferol-3β-ethoxycarbonate. This residue was named as L-No.3.

(d) The fourth reaction:-

224 mg of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene recovered in the third reaction (c) was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 10 minutes at 10°C in an atmosphere of argon using a 200 W high pressure mercury lamp, 654A-36 trademark for a product of Hanovia Company (conversion: 60%, at the final reaction, the remained hydroxycholesta-5,7- diene was converted to the previtamin D₃ compound as much as possible).
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure to afford the oily residue containing 1α-ethoxycarbonyloxy-pre-cholecalciferol-3β-ethoxycarbonate.
This residue was named as L-No.4.

(2) Synthesis of 1α-ethoxycarbonyloxycholecalciferol-3β-ethoxycarbonate

The residues described above, containing 1a-ethoxycarbonyloxyprecholecalciferol-313-ethoxy- carbonate L-No.1 - No.4, were put together and dissolved in 400 ml of benzene, and isomerization was carried out for 7 hours at 60°C in an atmosphere of argon.
After the reaction, the benzene solution was evaporated off at 25°C under reduced pressure to afford the oily residue containing 1a-ethoxycarbonyloxycholecalciferol-3a-ethoxycarbonate. This crude product was used as the starting material in the next step (3) without purification.

(3) Synthesis of 1a-hydroxycholecalciferol

1a-ethoxycarbonyloxycholecalciferol-3a-ethoxycarbonate obtained in (2) above, was dissolved in a mixture of 20 ml of methyl alcohol and 20 ml of benzene, and 20 ml of 2N-methyl alcohol solution of potassium hydroxide was added dropwise to the mixture.
After the addition, the reaction was carried out at 60°C for 1 hour.
After the reaction, the reaction mixture was concentrated at 25°C under reduced pressure to afford a residual product. 200 ml of water was then added to the residue and the product was extracted with ethyl acetate (200 ml x 2). The ethyl acetate extracts were combined, washed with a dilute hydrochloric acid, a saturated aqueous solution of sodium carbonate and a saturated aqueous solution of sodium chloride, dried. over anhydrous sodium sulfate, filtered and evaporated off at reduced pressure to afford 684 mg of the oily residue containing la-hydroxycholecalciferol. This crude product was column-chromatographed using silica gel (eluted with a benzene-acetone mixed solvent) to afford 275 mg of 1α-hydroxycholecalciferol (yield: 34%).
Analysis of the product showed the following results.

Melting point: 141.5 to 142°C
UV spectrum:
265 nm (s = 17200)
High resolution mass spectrum: M⁺ 400.3358 (C₂₇H₄₄0₂)

Example 8

(1) Synthesis of 1α-ethoxycarbonyloxycholecalciferol-3β-ethoxycarbonate

272 mg (0.5 m mol) of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 5 minutes at 10°C in an atmosphere of argon using a 200 W high pressure mercury lamp, 654A-36 trademark for a product of Hanovia Company, (conversion 30%).
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure to afford a residual product. 272 mg (0.5 m mol) of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene was irradiated in the same way as described above.
The obtained residues in these reaction were put together, dissolved in 200 ml of benzene, and isomerization was carried out for 3 hours at 70°C in an atmosphere of argon. After the reaction, the benzene solution was evaporated off at 25°C under reduced pressure to afford the residue containing 1a-ethoxycarbonyloxycholecalciferol-3β-ethoxyca rbon ate.
Methyl alcohol (40 ml) cooled at 0°C was added to the residue. The residue was suspended to afford crystals and the resulting crystals, 286 mg of 1α,3β-diethoxycarbonyloxycholesta-5,7-diene, were removed by filtration. After the filtration, the filtrate was concentrated at 25°C under reduced pressure to afford the oily residue containing 1a-ethoxycarbonyloxycholecalciferol-3a-ethoxycarbonate. This crude product was used as the starting material in the next step (2) without purification.

(2) Synthesis of 1a-hydroxycholecalciferol

1α-ethoxycarbonyloxycholecalciferol-3β-ethoxycarbonate obtained above, was dissolved in a mixture of 10 ml of methyl alcohol and 10 ml of benzene, and 10 ml of 2N-methyl alcohol solution of potassium hydroxide was added dropwise to the mixture. After the addition, the reaction was carried out at 60°C for 1 hour.
The reaction mixture was concentrated at 25°C under reduced pressure to afford a residual product. 100 ml of water was then added to the residue and the product was extracted with ethyl acetate (100 ml x 3). The ethylacetate extracts were combined, washed with a dilute hydrochloric acid, a saturated aqueous solution of sodium carbonate and a saturated aqueous solution of sodium chloride, dried with anhydrous sodium sulfate, filtered and evaporated off at reduced pressure to afford 200 mg of the oily residue containing 1α-hydroxycholecalciferol.
This crude product was column-chromatographed using silica gel (eluted with a benzene-acetone mixture solvent) to afford 57 mg of la-hydroxycholecalciferol (yield 30%, based on 258 mg of 1a,3(3-diethoxy carbonyloxycholesta-5,7-diene used up). This product showed the same characteristics as an authentic 1a-hydroxycholecarciferol.

Comparative Example 4

(1) Synthesis of 1α-acetoxyprecholecalciferol-3β-acetate

A solution of 1α,3β-diacetoxycholesta-5,7-diene (242 mg, 0.5 m moles) in benzene (600 ml) was cooled, and irradiated for 22 minutes (conversion = 60%) under argon using a 200 W high pressure mercury lamp, 654A-36, trademark for a product of Hanovia Company. The resulting solution was concentrated under the reduced pressure at 25°C to afford a residual product. Using a 1α,3β-diacetoxycholesta-5,7-diene (1.21 g, 25 m moles), the same reaction as mentioned above was conducted five times. The obtained residual products were combined, and subjected to the next reaction without purification.

(2) Synthesis of 1α-acetoxycholecalciferol-3β-acetate

A solution of 1α-acetoxyprecholecalciferol-3β-acetate obtained in (1) above in benzene (800 ml) was heated at a bath temperature of 80°C for 2.5 hours under an atmosphere of argon. After the reaction, the solution was concentrated under the reduced pressure to afford an oily product containing la-acetoxy- precholecalciferol-3β-acetate. The oily product, without the purification, subjected to the next reaction.

(3) Synthesis of 1α-hydroxycholecalciferol

To a solution of the oily product obtained in (2) above in methanol, 2.5% potassium hydroxide (11.2 ml) was added dropwise at the room temperature with stirring, and the reaction was carried out at the room temperature for an additional 2 hours. After the reaction, the resulting mixture was concentrated under the reduced pressure at 25°C to afford a residual product. Water (62 ml) was then added to the residue and the product was extracted with ether (2 x 120 ml). The ether extracts were combined, washed with sodium chloride solution, dried over anhydrous sodium sulfate, filtrated and concentrated under reduced pressure 2.1 g of oily product. The product was chromatographed on a column of silica gel (Wokogd C-200, 75 g) and the column was eluted with benzene-ethyl acetate to give 233 mg (yield; 19.5%, based on 1α,3β-diacetoxycholesta-5,7-diene) of 1a-hydroxycholecalciferol.

Comparative Example 5

(1) Synthesis of 1α-acetoxycholecalciferol-3β-acetate

242 mg (0.5 m mol) of 1a,313-diacetoxycholesta-5,7-diene was dissolved in 600 ml of diethyl ether, and this solution was irradiated with ultraviolet rays for 5 minutes at 10°C in an atmosphere of argon using a 200 W high pressure mercury lamp, 654A-36 trademark for a product of Hanovia Company, (conversion 30%).
After the reaction, the ether solution was evaporated off at room temperature under reduced pressure to afford a residual product. Moreover 242 mg (0.5 m mol) of 1a,313-diacetoxycholesta-5,7-diene was irradiated in the same way as described above.
The obtained residues in these reaction were put together, dissolved in 200 ml of benzene, and isomerization was carried out for 3 hours at 70°C in an atmosphere of argon. After the reaction, the benzene solution was evaporated off at 25°C under reduced pressure to afford the residue containing 1α-acetoxy- < cholecalciferol-3β-acetate.
Methyl alcohol (40 ml) cooled at 0°C was added to the residue. The residue was subjected to suspension but not to afford crystals, and 1a,3a-diacetoxycholesta-5,7-diene could not be recovered.

Claims

1. A process for preparing hydroxycholesta-5,7-dienes of the following formula [II]

wherein R, and R₂ represent a lower alkoxycarbonyl group having up to 4 carbon atoms in the alkoxy group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group having up to 4 carbon atoms in the alkoxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group having up to 4 carbon atoms in the alkoxy group or a hydroxyl group,
which comprises reacting hydroxycholest-5-enes of the following formula [I]

wherein R₁, R₂, R₃ and R₄ are the same as defined above,
with an allylic brominating agent in an inert organic solvent, and then contacting the resulting reaction mixture with a dehydrobrominating agent.

2. A process for preparing active-type vitamin D₃ compounds of the following formula [IV]

wherein R₃' and R₄' independently represent a hydrogen atom or a hydroxyl group, which comprises:

(i) reacting a hydroxycholesta-5-ene with an allylic brominating agent in an inert organic solvent, and then contacting the resulting reaction mixture with a dehydrobrominating agent to obtain a hydroxy- cholesta-5;7-diene;

(ii) exposing the hydroxycholesta-5,7-diene to ultraviolet irradiation in an inert organic solvent to obtain a mixture of previtamin D₃ compound and the unchanged hydroxycholesta-5,7-diene;

(iii) separating the mixture into the previtamin D₃ compound and the unchanged hydroxycholesta-5,7- diene;

(iv) recycling unchanged hydroxycholesta-5,7-diene through the ultraviolet irradiation; and

(v) thermally isomerizing the previtamin D₃ compounds and splitting off the protective groups; characterised in that said hydroxycholesta-5-ene is of the following formula [I]

wherein R, and R₂ represent a lower alkoxycarbonyl group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group or a hydroxyl group;

that said hydroxycholesta-5,7-diene is of the following formula [II]

wherein R₁, R₂, R₃ and R₄ are the same as defined above;
and that said previtamin D₃ compound is of the following formula [III]

wherein R₁, R₂, R₃ and R₄ are the same as defined above.

3. A process for preparing active-type vitamin D₃ compounds of the following formula [IV]

wherein R₃' and R₄' independently represent a hydrogen atom or a hydroxyl group,
which comprises

(i) reacting a hydroxycholesta-5-ene with an allylic brominating agent in an inert organic solvent, and then contacting the resulting reaction mixture with a dehydrobrominating agent to obtain a hydroxy- cholesta-5,7-diene;

(ii) exposing the said hydroxycholesta-5,7-diene to ultraviolet irradiation in an inert organic solvent, then thermally isomerizing to obtain a mixture of protected active-type vitamin D₃ compounds and unchanged hydroxycholesta-5,7-diene;

(iii) separating the mixture into the protected active-type vitamin D₃ compounds and the unchanged hydroxycholesta-5,7-dienes;

(iv) recycling the unchanged hydroxycholesta-5,7-dienes through the ultraviolet irradiation; and

(v) splitting off the protective groups of the protected active-type vitamin D₃ compounds; characterised in that said hydroxycholesta-5-ene is of the following formula [I]

wherein R₁ and R₂ represent a lower alkoxycarbonyl group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group or a hydroxyl group;

that said hydroxycholesta-5,7-diene is of the following formula [II]

wherein R₁, R₂, R₃ and R₄ are the same as defined above; and that said protected active-type vitamin D₃ compound is of the followina formula [V]

wherein R₁, R₂, R₃ and R₄ are the same as defined above.

4. A process for preparing active-type vitamin D₃ compounds of the following formula [IV]

(i) exposing a hydroxycholesta-5,7-diene to ultraviolet irradiation in an inert organic solvent to obtain a mixture of a previtamin D₃ compound and unchanged hydroxycholesta-5,7-diene;

(ii) separating the mixture into the previtamin D₃ compound and the unchanged hydroxycholesta-5,7- diene;

(iii) recycling the unchanged hydroxycholesta-5,7-diene through the ultraviolet irradiation; and

(iv) thermally isomerizing the previtamin D₃ compound, and splitting off protective groups, characterised in that said hydroxycholesta-5,7-diene is of the following formula [II]

and that said previtamin D₃ compound is of the formula

wherein R₁, R₂, R₃ and R₄ are the same as defined above.

5. A process for preparing active-type vitamin D₃ compounds of the following formula [IV]

wherein R₃' and R₄' represent a hydrogen atom or a hydroxyl group, which comprises

(i) exposing a hydroxycholesta-5,7-diene to ultraviolet irradiation in an inert organic solvent, then thermally isomerizing to obtain a mixture of a protected active-type vitamin D₃ compound and the unchanged hydroxycholesta-5,7-diene;

(ii) separating the mixture into the protected active-type vitamin D₃ compound and the unchanged hydroxycholesta-5,7-diene;

(iv) splitting off the protective groups of the protected active-type vitamin D₃ compounds, characterised in that said hydroxycholesta-5,7-diene is of the following formula [II]

and that said protected active-type vitamin D₃ compound is of the following formula [IV]

wherein R₁, R₂, R₃ and R₄ are the same as defined above.

6. The process of any of claims 1 to 5 characterised in that R, and R₂ in the hydroxycholest-5-enes of formula [I] or the hydroxycholesta-5,7-dienes of formula [II] are a methoxycarbonyl or an ethoxycarbonyl group.

7. The process of any of claims 1 to 6 characterised in that the exposing of hydroxycholesta-5,7-dienes to ultraviolet irradiation is conducted until the conversion of the hydroxycholesta-5,7-dienes reaches 0.150%.

8. The process of any of claims 1 to 7 characterised in that the separation of the mixture of the previtamin D₃ compounds or the protected active-type vitamin D₃ compounds and the unchanged hydroxy- cholesta-5,7-dienes is accomplished by means of recrystallization or rinse.

9. Hydroxycholesta-5,7-dienes of the general formula

wherein R, and R₂ represent a lower alkoxycarbonyl group, R₃ represents a hydrogen atom or a lower alkoxycarbonyloxy group and R₄ represents a hydrogen atom, a lower alkoxycarbonyloxy group or a hydroxyl group.

10. Hydroxycholest-5-enes of the general formula

wherein R₁, R₂, R₃ and R₄ are as defined in claim 9.